1. Field of the Invention
The present invention relates to the simulation of the vehicle control forces felt by an operator. It relates more particularly to the simulation of the flight controls and the mechanical reactions transmitted to a pilot by such control devices. The present invention can be applied, not only to vehicle training systems but also to the actual vehicle controls. It can, thus, be advantageously applied to aircraft in artificial feel-force systems (AFS).
2. Discussion of the Prior Art
French Pat. No. 2,178,495, filed by the present applicant, relates to a control simulator in which the simulated reaction is produced by a servo-controlled, hydraulic actuator. The piston of this actuator moves a distance X which is proportional to the movement of the control device. A servo signal is obtained as a function of this movement by entirely analogue computing circuits.
One of the more important aspects of the simulator according to the instant invention, which also includes a servo-controlled, hydraulic actuator, is that the servo signal which depends on the distance X is obtained by digital calculation, filtering and multiplication without any difficulty in smoothing.
For reasons of cost, operational convenience, and safety, training in vehicle operation and control is now conventionally given, not with the vehicles themselves, but by means of training systems especially designed for this purpose. Aircraft, for example, whose operation requires the application of highly developed and complicated techniques and for which stringent safety conditions are demanded, can only be left in the hands of fully trained flight crews. The cost of training such crews would be exorbitant if a large part of the training was not replaced by instruction given on the ground, under much better conditions, by means of flight training systems.
These systems, commonly known as "flight simulators," are designed to faithfully reproduce the environmental conditions experienced in a real crew compartment. The simulated crew compartments are mounted on platforms and subjected to accelerations which are comparable to those encountered in normal flight. The desired motion is determined by computers, as a function of the presumed manoeuvres executed and the external conditions (windspeed and wind direction) which are programmed or initiated by an instructor during execution of an exercise. All aircraft instruments and controls are faithfully simulated with regard to their appearances, installation and apparent operation. The simulation can be performed, not only for the main flight controls in yaw, pitch and roll, but also for certain secondary controls, for example when taxiing on the ground (nosewheel steering control) or emergency controls (undercarriage control). The reaction of each of these controls is specific to the particular pilot-controlled aircraft and varies as a function of the type of manoeuvre, the mode of action of the control device and the operating status of the control considered. Clearly, a thorough knowledge of these reactions enables a pilot to better sense the behavior of the aircraft and to act accordingly on the controls. Faithful simulation of the reactions which are transmitted by the flight controls is, thus, essential in a complete flight training system.
An important feature which is required for flight-control simulators is the simulation of defective operation. Electronic systems are particularly suitable for such simulation because they are easily adaptable to the simulation of various types of aircraft.
In an aircraft, a control system comprises the pilot's controls (stick, wheel, pedals, etc.) which are located in the crew compartment, linkages (rods, levers, cables, etc.) which are located in the fuselage, and the control surfaces (ailerons, flaps, etc.) which are located on the wings. In large aircraft, the linkages also include hydraulic servocontrols and artificial feel systems (AFS's).
The amplitude of the aerodynamic forces and the complexity of the linkages respectively due to the speed and span of the aircraft make it impossible to operate the control surfaces directly. The necessary forces are, in fact, produced by hydraulic, servo-assisted controls whose irreversibility prevents the transmission of aerodynamic reactions back to the pilots' controls.
In order to provide the pilot with the reactions required for correct flying of the aircraft, AFS's, also known as feel-force systems, are located in the linkages before the servocontrols and transmit to the pilots' controls and therefore to the pilots forces similar to the real reactions of the control surfaces. The simulator in accordance with the invention is thus particularly suitable for producing an AFS.
In certain exceptional cases, flight control may be simulated by using the actual control system of an aircraft. This method is not widely used, however, because of the high cost of such control systems, for which high quality is required, and also because of the size of the linkages required for large aircraft. Moreover, the latter are often duplicated for safety reasons, which is in conflict with the compactness required of training systems.